FIG. 1 illustrates the architecture of an exemplary GPRS network 100 that is part of a GSM public land mobile network (PLMN). GSM mobile station (MS) 101 is in communication with base transceiver station (BTS) 102, which provides radio coverage for cell 103. Several BTSs (102, 104) together are controlled by one base station controller (BSC) 105. A BTS and BSC together form a base station subsystem (BSS). The voice traffic for the mobile stations in their respective cells is routed through mobile switching center (MSC) 106, which is connected to the public switched telephone network (PSTN) 108 through gateway mobile switching center (GMSC) 107.
Several data bases are used for call control and network management, including home location register (HLR) 109, MSC/visited location register (VLR) 110, authentication center (AUC) 111, and equipment identity register (EIR) 112. Permanent data, such as the user's profile, as well as temporary data, such as the user's current location, are stored in HLR 109. MSC/VLR 110 is associated with a group of location areas and stores data for those users who are currently in its area of responsibility. This includes parts of the permanent user data that have been transmitted from HLR 109 to MSC/VLR 110 for faster access. MSC/VLR 110 may also assign and store local data such as a temporary identification. AUC 111 generates and stores security-related data, such as keys used for authentication and encryption. EIR 112 registers equipment data rather than subscriber data.
In addition to telephone numbers, subscriber identifiers, and equipment identifiers, several other identifiers have been defined to help manage GSM subscriber mobility and for addressing the network elements. The international mobile station equipment identity (IMEI) uniquely identifies a mobile station similar to a serial number. The IMEI is allocated by the equipment manufacturer and registered by the network operator who stores it in the EIR. Each registered user is uniquely identified by an international mobile subscriber identity (IMSI), which is stored in the subscriber identity module (SIM). A mobile station can only be operated if a SIM with a valid IMSI is inserted into equipment with a valid IMEI.
A given subscriber is identified by a mobile subscriber ISDN number (MSISDN), which is assigned to the subscriber's SIM. A mobile station set can have several MSISDNs depending on the SIM that is installed. The VLR, which is responsible for the current location of a subscriber, can assign a temporary mobile subscriber identity (TMSI) which has only local significance in the area handled by the VLR. It is stored on the network side only in the VLR and is not passed to the HLR.
GPRS support nodes (GSN) integrate GPRS into GSM architecture. GSNs are responsible for the delivery and routing of data packets between mobile stations and external packet data networks (PDN). All GSNs are connected via an IP-based GPRS backbone network. Within the backbone, the GSNs encapsulate the PDN packets and transmit (tunnel) them using the GPRS Tunneling Protocol GTP. Serving GPRS support node (SGSN) 113 is responsible for the delivery of data packets from and to mobile stations, such as MS 101, within its service area. GPRS 113 performs packet routing and transfer, mobility management, such as attach/detach and location management, logical link management, and authentication and charging functions. A location register of SGSN 113 stores location information, such as current cell and current VLR, and user profiles, such as the IMSI or other addresses used in the packet data network, for all the GPRS users registered with SGSN 113.
Gateway GPRS support node (GGSN) 114 acts as an interface between the GPRS backbone network and external packet data network (PDN) 115. GGSN 114 converts GPRS packets coming from SGSN 113 into the appropriate packet data protocol (PDP) format, such as IP or X.25, and sends the packets out on PDN 115. In the other direction, PDP addresses of incoming data packets are converted to the GSM address of the destination user, such as MS 101. The re-addressed packets are sent to SGSN 113, which is serving MS 101. GGSN 114 stores the current SGSN address of the user and his or her profile in its location register.
There is a many-to-many relationship between SGSNs and GGSNs in a GPRS network. A single GGSN may serve as the interface to external packet data networks for several SGSNs. Alternatively, a single SGSN may route its packets over different GGSNs to reach different packet data networks. For example, SGSN 113 may be coupled to SGSN/GGSN 116 in a different PLMN 117.
FIG. 1 also illustrates the various ETSI-defined interfaces between the network nodes. The Gb interface connects BSC 105 with SGSN 113. The Gn interface connects SGSNs in the same PLMN. The Gp interface is used to connect SGSNs and GGSNs in separate PLMNs. The Gi interface connects the PLMN with external public or private PDNs, such as the Internet or corporate intranets. Using the Gf interface, SGSN 113 may query EIR 112 regarding the IMEI of a mobile station trying to register with the network.
HLR 109 stores the user profile, the current SGSN address, and the PDP address(es) for each GPRS user in the PLMN. The Gr interface is used to exchange this information between HLR 109 and SGSN 113. For example, SGSN 113 informs HLR 109 about the current location of MS 101. When MS 101 registers with a new SGSN, HLR 109 will send the user profile to the new SGSN. The Gc interface between GGSN 114 and HLR 109 may be used by GGSN 114 to query a user's location and profile in order to update its location register. MSC/VLR 110 may include functions and register entries that allow coordination between packet-switched (GPRS) and circuit-switched (conventional GSM) services. For this purpose, the Gs interface connects the data bases of SGSN 113 and MSC/VLR 110. The Gd interface interconnects SMS gateway MSC (SMS-GMSC) 118 with SGSN 113 to exchange short message service (SMS) messages via GPRS.
Before MS 101 can use GPRS services, it must register with SGSN 113 of the GPRS network. SGSN 113 checks if the user is authorized, copies the user profile from HLR 109 and assigns a packet temporary mobile subscriber identity (P-TMSI) to the user. This procedure is called GPRS attach. For mobile stations using both circuit switched and packet switched services it is possible to perform combined GPRS/IMSI attach procedures. The disconnection from the GPRS network is called GPRS detach. The mobile station or the network can initiate the GPRS detach.
After a successful GPRS attach, MS 101 must apply for one or more addresses used in PDN 115 to exchange data packets with devices, such as server 119, in external PDN 115. For example, MS 101 must be assigned an IP address if PDN 115 is an IP network. This address is called a PDP (Packet Data Protocol) address. For each session, a PDP context is created, which describes the characteristics of the session. The PDP context contains the PDP type, the PDP address assigned to the mobile station, the requested quality of service, and the address of GGSN 114 that serves as the access point to PDN 115. This context is stored in MS 101, SGSN 113, and GGSN 114. With an active PDP context, MS 101 is “visible” to external PDN 115 and is able to send and receive data packets. The mapping between the two addresses, PDP and IMSI, enables GGSN 114 to transfer data packets between PDN 115 and MS 101. A user may have several simultaneous PDP contexts active at a given time.
The allocation of the PDP address can be static or dynamic. In the first case, the network operator of the user's home-PLMN permanently assigns a PDP address to the user. In the second case, a PDP address is assigned to the user upon activation of a PDP context. The PDP address can be assigned by the operator of the user's home-PLMN (dynamic home-PLMN PDP address) or by the operator of the visited network (dynamic visited-PLMN PDP address). The home network operator decides which of the possible alternatives may be used. In case of dynamic PDP address assignment, the GGSN is responsible for the allocation and the activation/deactivation of the PDP addresses.
It is difficult to monitor and track related GPRS packets as they are communicated on different interfaces between various network nodes. This is because each packet may include different parameters. Accordingly, there is a need in the prior art to correlate packets that are exchanged in the GPRS network.